From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id E2ED59863C3 for ; Tue, 3 Aug 2021 06:51:29 +0000 (UTC) From: Cornelia Huck In-Reply-To: References: <20210726165254.8529-1-mgurtovoy@nvidia.com> <20210728083306-mutt-send-email-mst@kernel.org> <20210730032625-mutt-send-email-mst@kernel.org> <0bffb13f-4e88-266d-e072-bafa44ec86fe@nvidia.com> <20210731175617-mutt-send-email-mst@kernel.org> <8360728a-68e7-3727-be2c-20b3a259a633@nvidia.com> <874kc727pi.fsf@redhat.com> <738e1458-2a54-f534-df62-3be198487e91@nvidia.com> <20210802130043-mutt-send-email-mst@kernel.org> <87y29jyrc5.fsf@redhat.com> Date: Tue, 03 Aug 2021 08:51:17 +0200 Message-ID: <87v94nyqai.fsf@redhat.com> MIME-Version: 1.0 Subject: [virtio-comment] Re: [RFC PATCH v2 1/2] Add virtio Admin Virtqueue specification Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable To: Jason Wang , "Michael S. Tsirkin" , Max Gurtovoy Cc: virtio-comment@lists.oasis-open.org, stefanha@redhat.com, oren@nvidia.com, parav@nvidia.com, shahafs@nvidia.com, eperezma@redhat.com, aadam@redhat.com, bodong@nvidia.com, amikheev@nvidia.com List-ID: On Tue, Aug 03 2021, Jason Wang wrote: > =E5=9C=A8 2021/8/3 =E4=B8=8B=E5=8D=882:28, Cornelia Huck =E5=86=99=E9=81= =93: >> On Mon, Aug 02 2021, "Michael S. Tsirkin" wrote: >> >>> On Mon, Aug 02, 2021 at 07:03:11PM +0300, Max Gurtovoy wrote: >>>> There is no much bits left in the generic feature field for all the fe= atures >>>> we would like to add. >>>> I mentioned only 5-6 in the above example and it will bring us to bit = 46 >>>> already. >>>> >>>> please think of 5-10 years from today. >>>> >>> IIUC nothing prevents adding more once we exhaust 64 bits. IMHO it's ac= tually >>> pretty important to make sure the feature negotiation works well >>> and covers relevant usecases. If we have limitations preventing that >>> I'd like to at least try to fix that not replacing feature negotiation = with >>> something else. >> I recall that we had a discussion about that years ago when we >> introduced VERSION_1; we explicitly agreed that we can extend features >> beyond 64 bit once we need it. (A quick search did not turn up that mail >> exchange, though.) >> > > E.g PCI transport has feature_select. > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 le32 device_feature_select;= =C2=A0=C2=A0=C2=A0=C2=A0 /* read-write */ > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 le32 device_feature;=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* read-only for = driver */ > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 le32 driver_feature_select;= =C2=A0=C2=A0=C2=A0=C2=A0 /* read-write */ > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 le32 driver_feature;=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* read-write */ > > Technically it can support 32*32 different features. MMIO uses a similar scheme; CCW uses struct virtio_feature_desc { le32 features; u8 index; }; so there's plenty of room to spare. This publicly archived list offers a means to provide input to the=0D OASIS Virtual I/O Device (VIRTIO) TC.=0D =0D In order to verify user consent to the Feedback License terms and=0D to minimize spam in the list archive, subscription is required=0D before posting.=0D =0D Subscribe: virtio-comment-subscribe@lists.oasis-open.org=0D Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org=0D List help: virtio-comment-help@lists.oasis-open.org=0D List archive: https://lists.oasis-open.org/archives/virtio-comment/=0D Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf= =0D List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lis= ts=0D Committee: https://www.oasis-open.org/committees/virtio/=0D Join OASIS: https://www.oasis-open.org/join/